Matching network and power amplifier circuit

ABSTRACT

A matching network is a matching network of a power amplifier circuit that outputs a signal obtained by a differential amplifier amplifying power of a high-frequency signal. The matching network includes an input-side winding connected between differential outputs of the differential amplifier; an output-side winding that is coupled to the input-side winding via an electromagnetic field and whose one end is connected to a reference potential; a first LC series resonant circuit including a capacitive element and an inductive element connected in series with each other, and being connected in parallel with the input-side winding; and a second LC series resonant circuit including a capacitive element and an inductive element connected in series with each other, and being connected in parallel with the output-side winding.

This is a continuation of U.S. patent application Ser. No. 16/217,506filed on Dec. 12, 2018, which claims priority from Japanese PatentApplication No. 2017-252513 filed on Dec. 27, 2017. The contents ofthese applications are incorporated herein by reference in theirentireties.

BACKGROUND

The present disclosure relates to a matching network and a poweramplifier circuit. In recent years, in radio communication systems inmobile communication terminal devices, such as, cellular phones andsmartphones, modulation schemes, such as high speed uplink packet access(HSUPA) and long term evolution (LTE), have been adopted. In a fourthgeneration mobile communication system, multiband carrier waves areincreasingly used, and the support for a plurality of frequency bands isdemanded. Furthermore, to achieve high-speed data communication andstabilization of communication, a bandwidth is widened by carrieraggregation (CA). For this reason, in a power amplifier circuit at astage previous to a front-end section as well, support for multiplebands and wider bandwidths is demanded.

U.S. Pat. No. 9,584,076 discloses a power amplifier module including adifferential amplifier and a transformer for output matching. Such aconfiguration makes it possible to achieve output matching over a widefrequency band. Furthermore, for example, a decoupling capacitor betweencircuits is unnecessary, thereby enabling a reduction in the size orcost of the power amplifier module.

In a typical mobile communication terminal device, an amplifier elementconstituting a power amplifier circuit has nonlinear gaincharacteristics and nonlinear phase characteristics to cause distortionin a high-frequency signal, and outputs a signal containing a harmonic.Although, in the case where the power amplifier circuit includes adifferential amplifier and a transformer, it is possible to achieveoutput matching over a wide frequency band as described above, aharmonic caused by the nonlinearity of the amplifier element tends to beoutput.

BRIEF SUMMARY

In view of the above, the present disclosure has been made to make itpossible to suppress a harmonic output from a power amplifier circuit.

A matching network according to one embodiment of the present disclosureis a matching network of a power amplifier circuit to which ahigh-frequency signal is input from an input node and that outputs, toan output node, a signal obtained by a differential amplifier amplifyingpower of the high-frequency signal. The matching network includes atransformer including an input-side winding connected betweendifferential outputs of the differential amplifier, and an output-sidewinding that is coupled to the input-side winding via an electromagneticfield and whose one end is connected to a reference potential; a firstLC series resonant circuit including a capacitive element and aninductive element connected in series with each other, and beingconnected in parallel with the input-side winding; and a second LCseries resonant circuit including a capacitive element and an inductiveelement connected in series with each other, and being connected inparallel with the output-side winding.

In this configuration, resonant frequencies of the first LC seriesresonant circuit and the second LC series resonant circuit are caused tocoincide with the frequency of any harmonic of a plurality of harmonics,and thus the matching network can effectively suppress a harmonic outputfrom the power amplifier circuit.

Other features, elements, characteristics and advantages of the presentdisclosure will become more apparent from the following detaileddescription of embodiments of the present disclosure with reference tothe attached drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates an example of a configuration of a power amplifiercircuit according to a first embodiment;

FIG. 2 illustrates an example of a schematic configuration of adifferential amplifier;

FIG. 3 illustrates another example of the schematic configuration of thedifferential amplifier;

FIG. 4 illustrates an example of a configuration of a power amplifiercircuit according to a comparative example;

FIG. 5 illustrates an example of a bandpass characteristic in thecomparative example illustrated in FIG. 4;

FIG. 6 illustrates an example of a bandpass characteristic in theexample of the configuration illustrated in FIG. 1;

FIG. 7 illustrates an example of a configuration of a power amplifiercircuit according to a second embodiment;

FIG. 8 illustrates an example of a bandpass characteristic in theexample of the configuration illustrated in FIG. 7;

FIG. 9 illustrates an example of a configuration of a power amplifiercircuit according to a third embodiment;

FIG. 10 illustrates an example of a bandpass characteristic in theexample of the configuration illustrated in FIG. 9;

FIG. 11 illustrates an example of a configuration of a power amplifiercircuit according to a fourth embodiment;

FIG. 12 illustrates an example of a bandpass characteristic in theexample of the configuration illustrated in FIG. 11; and

FIG. 13 illustrates an example of a configuration of a power amplifiercircuit according to a fifth embodiment.

DETAILED DESCRIPTION

A matching network and a power amplifier circuit according toembodiments will be described in detail below with reference to thedrawings. Note that the present disclosure is not to be limited by theseembodiments. The embodiments are merely illustrative, and it goeswithout necessarily saying that configurations described in differentembodiments can be partially replaced or combined. In second andsubsequent embodiments, descriptions of things in common with a firstembodiment are omitted, and only respects in which the second andsubsequent embodiments differ from the first embodiment will bedescribed. In particular, similar operation and effects based on similarconfigurations are not referred to for each embodiment.

First Embodiment

FIG. 1 illustrates an example of a configuration of a power amplifiercircuit according to the first embodiment. A power amplifier circuit 1can be used in a mobile communication terminal device, such as acellular phone or smartphone, to transmit various signals, such as voiceand data, to a base station.

The power amplifier circuit 1 amplifies an input signal RF_(IN), whichis a high-frequency signal, input from a previous-stage circuit to aninput node 2. Subsequently, the power amplifier circuit 1 outputs anoutput signal RF_(OUT), which is the amplified high-frequency signal,from an output node 3 to a subsequent-stage circuit. Although an exampleof the previous-stage circuit is a transmission power control circuitthat adjusts the power of a modulated signal, the previous-stage circuitis not limited to this. Although an example of the subsequent-stagecircuit is a front-end circuit that performs, for example, filtering onthe output signal RF_(OUT) to transmit the output signal RF_(OUT)subjected to filtering to an antenna, the subsequent-stage circuit isnot limited to this. Although an example of the frequency of afundamental (carrier wave) of a high-frequency signal ranges from aboutseveral hundred MHz to about several GHz, the frequency is not limitedto the range.

As illustrated in FIG. 1, the power amplifier circuit 1 includes adifferential amplifier 4, a first transformer 5, a second transformer 6,a first LC series resonant circuit 7, and a second LC series resonantcircuit 8.

The first transformer 5 constitutes an input matching network between anoutput of the previous-stage circuit previous to the power amplifiercircuit 1 and an input of the power amplifier circuit 1.

The first transformer 5 includes an input-side winding 51 and anoutput-side winding 52.

One end of the input-side winding 51 is connected to a referencepotential. The other end of the input-side winding 51 is connected tothe input node 2. Although the reference potential herein is a groundpotential, the reference potential is not limited to this.

The output-side winding 52 is connected between an input IN_(P) and aninput IN_(N) of the differential amplifier 4.

The input-side winding 51 and the output-side winding 52 are coupled viaan electromagnetic field. Thus, the input signal RF_(IN) input from theinput node 2 to the other end of the input-side winding 51 is convertedinto a differential signal by the first transformer 5 and is output tothe differential amplifier 4.

The second transformer 6 constitutes a matching network (output matchingnetwork) 100 between an output of the power amplifier circuit 1 and aninput of the subsequent-stage circuit subsequent to the power amplifiercircuit 1.

The second transformer 6 includes an input-side winding 61 and anoutput-side winding 62.

The input-side winding 61 is connected between an output OUT_(N) and anoutput OUT_(P) of the differential amplifier 4. A power-supply potentialV_(CC) is connected to a midpoint of the input-side winding 61.Furthermore, a capacitor C_(IN) is connected in parallel with theinput-side winding 61.

One end of the output-side winding 62 is connected to the referencepotential. The other end of the output-side winding 62 is connected tothe output node 3. Furthermore, a capacitor C_(OUT) is connected inparallel with the output-side winding 62.

The input-side winding 61 and the output-side winding 62 are coupled viaan electromagnetic field. Thus, the differential signal output from thedifferential amplifier 4 is converted into the output signal RF_(OUT) bythe second transformer 6 and is output from the output node 3.

The first LC series resonant circuit 7 includes a capacitor C₁ servingas a capacitive element, and an inductor L₁ serving as an inductiveelement.

The first LC series resonant circuit 7 is constituted by the capacitorC₁ and the inductor L₁ that are connected in series with each other.Furthermore, the first LC series resonant circuit 7 is connected inparallel with the input-side winding 61 of the second transformer 6.

The second LC series resonant circuit 8 includes a capacitor C₂ servingas a capacitive element, and an inductor L₂ serving as an inductiveelement.

The second LC series resonant circuit 8 is constituted by the capacitorC₂ and the inductor L₂ that are connected in series with each other.Furthermore, the second LC series resonant circuit 8 is connected inparallel with the output-side winding 62 of the second transformer 6.

In the power amplifier circuit 1 according to the first embodiment, thefirst LC series resonant circuit 7, the second LC series resonantcircuit 8, and the input-side winding 61 and the output-side winding 62of the second transformer 6 operate as the matching network 100.

Here, a configuration of the differential amplifier 4 will be described.FIG. 2 illustrates an example of a schematic configuration of thedifferential amplifier. FIG. 3 illustrates another example of theschematic configuration of the differential amplifier.

As illustrated in FIGS. 2 and 3, the differential amplifier 4 includes adifferential pair of transistors Tr₄₁ and Tr₄₂, resistors R₄₁ and R₄₂,and a bias circuit 41.

The transistors Tr₄₁ and Tr₄₂ may be, for example, bipolar transistorsas illustrated in FIG. 2, or may be, for example, field-effecttransistors (FETs) as illustrated in FIG. 3. In the case where thetransistors Tr₄₁ and Tr₄₂ are constituted by bipolar transistors,heterojunction bipolar transistors (HBTs) are given as an example.

The bias circuit 41 is connected to a power-supply potential V_(BAT).Although the configuration of the bias circuit 41 including, forexample, a transistor for supply of bias current (not illustrated) andso forth is given as an example, the present disclosure is not limitedby the configuration of the bias circuit 41. For example, in theexamples illustrated in FIGS. 2 and 3, the configurations of the biascircuit 41 may differ from each other.

The case where the transistors Tr₄₁ and Tr₄₂ constituting thedifferential amplifier 4 are HBTs will be described with reference toFIG. 2.

Emitters of the transistors Tr₄₁ and Tr₄₂ are connected to the referencepotential. A collector of the transistor Tr₄₁ is connected to the outputOUT_(N). A collector of the transistor Tr₄₂ is connected to the outputOUT_(P). The power-supply potential V_(CC) is supplied to the collectorsof the transistors Tr₄₁ and Tr₄₂ via the input-side winding 61 of thesecond transformer 6 (see FIG. 1).

A base of the transistor Tr₄₁ is connected to the input IN_(P). The biascircuit 41 supplies a bias current to the base of the transistor Tr₄₁via the resistor R₄₁. Furthermore, a base of the transistor Tr₄₂ isconnected to the input IN_(N). The bias circuit 41 supplies a biascurrent to the base of the transistor Tr₄₂ via the resistor R₄₂.

The case where the transistors Tr₄₁ and Tr₄₂ constituting thedifferential amplifier 4 are FETs will be described with reference toFIG. 3.

Sources of the transistors Tr₄₁ and Tr₄₂ are connected to the referencepotential. A drain of the transistor Tr₄₁ is connected to the outputOUT_(N). A drain of the transistor Tr₄₂ is connected to the outputOUT_(P). The power-supply potential V_(CC) is supplied to the drains ofthe transistors Tr₄₁ and Tr₄₂ via the input-side winding 61 of thesecond transformer 6 (see FIG. 1).

A gate of the transistor Tr₄₁ is connected to the input IN_(P). The biascircuit 41 supplies a bias potential to the gate of the transistor Tr₄₁via the resistor R₄₁. Furthermore, a gate of the transistor Tr₄₂ isconnected to the input IN_(N). The bias circuit 41 supplies a biaspotential to the gate of the transistor Tr₄₂ via the resistor R₄₂.

Note that the transistors Tr₄₁ and Tr₄₂ constituting the differentialamplifier 4 are not limited to the above-described HBTs or FETs.

FIG. 4 illustrates an example of a configuration of a power amplifiercircuit according to a comparative example. FIG. 5 illustrates anexample of a bandpass characteristic in the comparative exampleillustrated in FIG. 4. FIG. 6 illustrates an example of a bandpasscharacteristic in the example of the configuration illustrated in FIG.1.

The power amplifier circuit according to the comparative exampleillustrated in FIG. 4 differs from the power amplifier circuit 1according to the first embodiment illustrated in FIG. 1 in that thepower amplifier circuit according to the comparative example does notinclude the first LC series resonant circuit 7 and the second LC seriesresonant circuit 8.

In the examples illustrated in FIGS. 5 and 6, the horizontal axisrepresents frequency, and the vertical axis represents gain. A solidline illustrated in FIG. 6 represents a bandpass characteristic of anetwork through which a differential output of the differentialamplifier 4 is transmitted to the output node 3 in the configurationaccording to the first embodiment illustrated in FIG. 1. A dashed lineillustrated in FIG. 6 represents a bandpass characteristic of thenetwork through which an in-phase output of the differential amplifier 4is transmitted to the output node 3 in the configuration according tothe first embodiment illustrated in FIG. 1. A solid line illustrated inFIG. 5 represents a bandpass characteristic of a network through which adifferential output of the differential amplifier 4 is transmitted tothe output node 3 in the configuration according to the comparativeexample illustrated in FIG. 4. A dashed line illustrated in FIG. 5represents a bandpass characteristic of the network through which anin-phase output of the differential amplifier 4 is transmitted to theoutput node 3 in the configuration according to the comparative exampleillustrated in FIG. 4.

Furthermore, a symbol “f₁” illustrated in FIGS. 5 and 6 represents afrequency of a fundamental of a high-frequency signal. A symbol “f₂”illustrated in FIGS. 5 and 6 represents a frequency of a second harmonicof the high-frequency signal. A symbol “f₃” illustrated in FIGS. 5 and 6represents a frequency of a third harmonic of the high-frequency signal.

In the configuration of the power amplifier circuit according to thecomparative example illustrated in FIG. 4, a combination of thedifferential amplifier 4 and the second transformer 6 makes it possibleto achieve output matching over a wide frequency band. As illustrated inFIG. 5, this makes it possible to achieve a wide bandpass characteristicin a frequency band including the fundamental.

Although, in the configuration of the power amplifier circuit accordingto the comparative example illustrated in FIG. 4, a wide bandpasscharacteristic is achieved, a harmonic caused by the nonlinearity of thetransistors Tr₄₁ and Tr₄₂ constituting the differential amplifier 4tends to be output.

In the power amplifier circuit 1 according to the first embodiment, withrespect to the matching network 100, the first LC series resonantcircuit 7 is connected in parallel with the input-side winding 61 of thesecond transformer 6. Furthermore, in the power amplifier circuit 1according to the first embodiment, with respect to the matching network100, the second LC series resonant circuit 8 is connected in parallelwith the output-side winding 62 of the second transformer 6. Resonantfrequencies of the first LC series resonant circuit 7 and the second LCseries resonant circuit 8 are caused to coincide with the frequency ofany harmonic of a plurality of harmonics, thereby making it possible tosuppress a harmonic output from the power amplifier circuit 1. Anexample of setting of resonant frequencies of the first LC seriesresonant circuit 7 and the second LC series resonant circuit 8 will bedescribed below.

In the power amplifier circuit 1 according to the first embodiment, thedifferential amplifier 4 is used, and thus a load impedance seen fromthe differential amplifier 4 is open-circuited at even harmonicsincluding the second harmonic. Thus, in terms of the highly efficientoperation of the differential amplifier 4, it is desirable that aresonant frequency of the first LC series resonant circuit 7 is causedto coincide with the frequency of a harmonic other than even harmonics,that is, the frequency of an odd harmonic.

A resonant frequency f_(LC1) of the first LC series resonant circuit 7is represented by the following equation (1).

$\begin{matrix}{f_{{LC}\; 1} = \frac{1}{2\pi\sqrt{L_{1}C_{1}}}} & (1)\end{matrix}$

The resonant frequency f_(LC1) of the first LC series resonant circuit 7is set in a first frequency band a including the third harmonic, forexample, (see FIG. 6). Specifically, it is desirable that the frequencyrange of the first frequency band a is not less than about 0.85 timesand not more than about 1.15 times the frequency f₃ of the thirdharmonic. Thus, as illustrated in FIG. 6, the matching network 100according to the first embodiment can suppress the third harmonic in thebandpass characteristic of the network through which a differentialoutput of the differential amplifier 4 is transmitted to the output node3.

At this time, it is desirable that the capacitor C₁ and the inductor L₁are determined so that the resonant frequency f_(LC1) of the first LCseries resonant circuit 7 coincides with the frequency f₃ of the thirdharmonic. This makes it possible to more effectively suppress the thirdharmonic in the bandpass characteristic of the network through which adifferential output of the differential amplifier 4 is transmitted tothe output node 3.

Furthermore, at this time, the load impedance seen from the differentialamplifier 4 is open-circuited at even harmonics including the secondharmonic by the differential operation of the differential amplifier 4as described above and is short-circuited at the third harmonic by thefirst LC series resonant circuit 7. Thus, the differential amplifier 4performs inverse class-F operation, thereby enabling highly efficientoperation.

Furthermore, a resonant frequency f_(LC2) of the second LC seriesresonant circuit 8 is represented by the following equation (2).

$\begin{matrix}{f_{{LC}\; 2} = \frac{1}{2\pi\sqrt{L_{2}C_{2}}}} & (2)\end{matrix}$

The resonant frequency f_(LC2) of the second LC series resonant circuit8 is set in a second frequency band b including the second harmonic, forexample, (see FIG. 6). Specifically, it is desirable that the frequencyrange of the second frequency band b is not less than about 0.85 timesand not more than about 1.15 times the frequency f₂ of the secondharmonic. Thus, as illustrated in FIG. 6, the matching network 100according to the first embodiment can suppress the second harmonic inthe bandpass characteristic of the network through which a differentialoutput of the differential amplifier 4 is transmitted to the output node3 and in the bandpass characteristic of the network through which anin-phase output of the differential amplifier 4 is transmitted to theoutput node 3.

At this time, it is desirable that the capacitor C₂ and the inductor L₂are determined so that the resonant frequency f_(LC2) of the second LCseries resonant circuit 8 coincides with the frequency f₂ of the secondharmonic. This makes it possible to more effectively suppress the secondharmonic in the bandpass characteristic of the network through which adifferential output of the differential amplifier 4 is transmitted tothe output node 3 and in the bandpass characteristic of the networkthrough which an in-phase output of the differential amplifier 4 istransmitted to the output node 3.

Note that the resonant frequency f_(LC1) of the first LC series resonantcircuit 7 and the resonant frequency f_(LC2) of the second LC seriesresonant circuit 8 are not to be limited to the above-described examplesand are to be appropriately determined in accordance with a level ofeach harmonic generated in the power amplifier circuit 1.

For example, the resonant frequency f_(LC1) of the first LC seriesresonant circuit 7 may be set in a first frequency band including anyone of odd harmonics of fifth and higher orders. The resonant frequencyf_(LC2) of the second LC series resonant circuit 8 may be set in asecond frequency band including any one of harmonics of third and higherorders.

Furthermore, for example, the resonant frequency f_(LC1) of the first LCseries resonant circuit 7 and the resonant frequency f_(LC2) of thesecond LC series resonant circuit 8 may be set so that the same harmonicis suppressed. In this case, the first frequency band and the secondfrequency band may be the same frequency band.

Second Embodiment

FIG. 7 illustrates an example of a configuration of a power amplifiercircuit according to a second embodiment. Components that are the sameas those in the first embodiment are denoted by the same referencenumerals, and description thereof is omitted.

In contrast to the power amplifier circuit 1 according to the firstembodiment, a power amplifier circuit 1 a according to the secondembodiment further includes, as a matching network 100 a, an LC parallelresonant circuit 9 in addition to the first LC series resonant circuit 7and the second LC series resonant circuit 8.

The LC parallel resonant circuit 9 includes a capacitor C₃ serving as acapacitive element, and an inductor L₃ serving as an inductive element.

The LC parallel resonant circuit 9 is constituted by the capacitor C₃and the inductor L₃ that are connected in parallel with each otherbetween the other end of the output-side winding 62 of the secondtransformer 6 and the output node 3.

FIG. 8 illustrates an example of a bandpass characteristic in theexample of the configuration illustrated in FIG. 7.

In the example illustrated in FIG. 8, the horizontal axis representsfrequency, and the vertical axis represents gain. A solid lineillustrated in FIG. 8 represents a bandpass characteristic of a networkthrough which a differential output of the differential amplifier 4 istransmitted to the output node 3 in the configuration according to thesecond embodiment illustrated in FIG. 7. A dashed line illustrated inFIG. 8 represents a bandpass characteristic of the network through whichan in-phase output of the differential amplifier 4 is transmitted to theoutput node 3 in the configuration according to the second embodimentillustrated in FIG. 7.

Furthermore, a symbol “f₁” illustrated in FIG. 8 represents a frequencyof a fundamental of a high-frequency signal. A symbol “f₂” illustratedin FIG. 8 represents a frequency of a second harmonic of thehigh-frequency signal. A symbol “f₃” illustrated in FIG. 8 represents afrequency of a third harmonic of the high-frequency signal.

A resonant frequency f_(LC3) of the LC parallel resonant circuit 9 isrepresented by the following equation (3).

$\begin{matrix}{f_{{LC}\; 3} = \frac{1}{2\pi\sqrt{L_{3}C_{3}}}} & (3)\end{matrix}$

The resonant frequency f_(LC3) of the LC parallel resonant circuit 9 isset in a third frequency band c including the third harmonic, forexample, (see FIG. 8). Specifically, it is desirable that the frequencyrange of the third frequency band c is not less than about 0.85 timesand not more than about 1.15 times the frequency f₃ of the thirdharmonic. Thus, as illustrated in FIG. 8, the matching network 100 aaccording to the second embodiment can suppress, in comparison with thefirst embodiment, the third harmonic in the bandpass characteristic ofthe network through which a differential output of the differentialamplifier 4 is transmitted to the output node 3 and in the bandpasscharacteristic of the network through which an in-phase output of thedifferential amplifier 4 is transmitted to the output node 3.

At this time, it is desirable that the capacitor C₃ and the inductor L₃are determined so that the resonant frequency f_(LC3) of the LC parallelresonant circuit 9 coincides with the frequency f₃ of the thirdharmonic. This makes it possible to still more effectively suppress thethird harmonic in the bandpass characteristic of the network throughwhich a differential output of the differential amplifier 4 istransmitted to the output node 3 and in the bandpass characteristic ofthe network through which an in-phase output of the differentialamplifier 4 is transmitted to the output node 3.

Note that the resonant frequency f_(LC3) of the LC parallel resonantcircuit 9 is not to be limited to the above-described example and is tobe appropriately determined in accordance with a level of each harmonicgenerated in the power amplifier circuit 1 a.

For example, the resonant frequency f_(LC3) of the LC parallel resonantcircuit 9 may be set in a third frequency band including any one ofharmonics of second or fourth and higher orders.

Furthermore, for example, the resonant frequency f_(LC3) of the LCparallel resonant circuit 9 may be set so that a harmonic with the samefrequency as the resonant frequency f_(LC1) of the first LC seriesresonant circuit 7 or the resonant frequency f_(LC2) of the second LCseries resonant circuit 8 is suppressed. In this case, the thirdfrequency band may be the same as the first frequency band or the secondfrequency band.

Third Embodiment

FIG. 9 illustrates an example of a configuration of a power amplifiercircuit according to a third embodiment. Components that are the same asthose in the first embodiment are denoted by the same referencenumerals, and description thereof is omitted.

In contrast to the power amplifier circuit 1 according to the firstembodiment, a power amplifier circuit 1 b according to the thirdembodiment further includes, as a matching network 100 b, an LC highpass filter circuit 10 in addition to the first LC series resonantcircuit 7 and the second LC series resonant circuit 8.

The LC high pass filter circuit 10 includes a capacitor C₄ serving as acapacitive element, and an inductor L₄ serving as an inductive element.

The LC high pass filter circuit 10 is constituted by the capacitor C₄connected between the other end of the output-side winding 62 of thesecond transformer 6 and the output node 3, and the inductor L₄connected between the output node 3 and the reference potential.

FIG. 10 illustrates an example of a bandpass characteristic in theexample of the configuration illustrated in FIG. 9.

In the example illustrated in FIG. 10, the horizontal axis representsfrequency, and the vertical axis represents gain. A solid lineillustrated in FIG. 10 represents a bandpass characteristic of a networkthrough which a differential output of the differential amplifier 4 istransmitted to the output node 3 in the configuration according to thethird embodiment illustrated in FIG. 9. A dashed line illustrated inFIG. 10 represents a bandpass characteristic of the network throughwhich an in-phase output of the differential amplifier 4 is transmittedto the output node 3 in the configuration according to the thirdembodiment illustrated in FIG. 9.

Furthermore, a symbol “f₁” illustrated in FIG. 10 represents a frequencyof a fundamental of a high-frequency signal. A symbol “f₂” illustratedin FIG. 10 represents a frequency of a second harmonic of thehigh-frequency signal. A symbol “f₃” illustrated in FIG. 10 represents afrequency of a third harmonic of the high-frequency signal.

A cutoff frequency f_(C1) of the LC high pass filter circuit 10 isrepresented by the following equation (4).

$\begin{matrix}{f_{C\; 1} = \frac{1}{2\pi\sqrt{L_{4}C_{4}}}} & (4)\end{matrix}$

The cutoff frequency f_(C1) of the LC high pass filter circuit 10 is setin a frequency band lower than the fundamental of the high-frequencysignal (see FIG. 10). Thus, as illustrated in FIG. 10, the matchingnetwork 100 b according to the third embodiment can suppresslow-frequency oscillation generated through a power-supply loop or thelike without necessarily attenuating the fundamental of thehigh-frequency signal in the bandpass characteristic of the networkthrough which a differential output of the differential amplifier 4 istransmitted to the output node 3.

Fourth Embodiment

FIG. 11 illustrates an example of a configuration of a power amplifiercircuit according to a fourth embodiment. Components that are the sameas those in the first embodiment are denoted by the same referencenumerals, and description thereof is omitted.

In contrast to the power amplifier circuit 1 according to the firstembodiment, a power amplifier circuit 1 c according to the fourthembodiment further includes, as a matching network 100 c, an LC low passfilter circuit 11 in addition to the first LC series resonant circuit 7and the second LC series resonant circuit 8.

The LC low pass filter circuit 11 includes an inductor L₅ serving as aninductive element, and a capacitor C₅ serving as a capacitive element.

The LC low pass filter circuit 11 is constituted by the inductor L₅connected between the other end of the output-side winding 62 of thesecond transformer 6 and the output node 3, and the capacitor C₅connected between the output node 3 and the reference potential.

FIG. 12 illustrates an example of a bandpass characteristic in theexample of the configuration illustrated in FIG. 11.

In the example illustrated in FIG. 12, the horizontal axis representsfrequency, and the vertical axis represents gain. A solid lineillustrated in FIG. 12 represents a bandpass characteristic of a networkthrough which a differential output of the differential amplifier 4 istransmitted to the output node 3 in the configuration according to thefourth embodiment illustrated in FIG. 11. A dashed line illustrated inFIG. 12 represents a bandpass characteristic of the network throughwhich an in-phase output of the differential amplifier 4 is transmittedto the output node 3 in the configuration according to the fourthembodiment illustrated in FIG. 11.

Furthermore, a symbol “f₁” illustrated in FIG. 12 represents a frequencyof a fundamental of a high-frequency signal. A symbol “f₂” illustratedin FIG. 12 represents a frequency of a second harmonic of thehigh-frequency signal. A symbol “f₃” illustrated in FIG. 12 represents afrequency of a third harmonic of the high-frequency signal.

A cutoff frequency f_(C2) of the LC low pass filter circuit 11 isrepresented by the following equation (5).

$\begin{matrix}{f_{C\; 2} = \frac{1}{2\pi\sqrt{L_{5}C_{5}}}} & (5)\end{matrix}$

The cutoff frequency f_(C2) of the LC low pass filter circuit 11 is setin a frequency band higher than the fundamental of the high-frequencysignal (see FIG. 12). Thus, as illustrated in FIG. 12, the matchingnetwork 100 c according to the fourth embodiment can suppress, incomparison with the first embodiment, the second harmonic, the thirdharmonic, and so forth without necessarily attenuating the fundamentalof the high-frequency signal in the bandpass characteristic of thenetwork through which a differential output of the differentialamplifier 4 is transmitted to the output node 3.

Fifth Embodiment

FIG. 13 illustrates an example of a configuration of a power amplifiercircuit according to a fifth embodiment. Components that are the same asthose in the first embodiment are denoted by the same referencenumerals, and description thereof is omitted.

A power amplifier circuit 1 d according to the fifth embodiment differsfrom the power amplifier circuit 1 according to the first embodiment inthat the power amplifier circuit 1 d has a two-stage configurationcomposed of differential amplifiers 4 a and 4 b.

In the power amplifier circuit 1 d according to the fifth embodiment, athird transformer 12 is provided between the first-stage differentialamplifier 4 a and the second-stage differential amplifier 4 b.

A configuration of the first-stage differential amplifier 4 a or aconfiguration of the second-stage differential amplifier 4 b may be thesame as the configuration of the differential amplifier 4 according tothe first to fourth embodiments or may differ from the configuration ofthe differential amplifier 4.

The third transformer 12 constitutes an interstage matching networkbetween an output of the first-stage differential amplifier 4 a and aninput of the second-stage differential amplifier 4 b.

The third transformer 12 includes an input-side winding 121 and anoutput-side winding 122.

The input-side winding 121 is connected between an output OUT_(N) and anoutput OUT of the differential amplifier 4 a. A midpoint of theinput-side winding 121 is connected to the power-supply potentialV_(CC).

The output-side winding 122 is connected between an input IN and aninput IN_(N) of the differential amplifier 4 b.

The input-side winding 121 and the output-side winding 122 are coupledvia an electromagnetic field. Thus, a differential signal output fromthe differential amplifier 4 a and input to the input-side winding 121is subjected to electromagnetic induction by the third transformer 12and is output to the differential amplifier 4 b.

Thus, the two-stage configuration composed of the differentialamplifiers 4 a and 4 b enables higher output power than theconfiguration according to the first to fourth embodiments.

Furthermore, for example, the differential amplifier 4 a and thedifferential amplifier 4 b are respectively caused to serve as adrive-stage amplifier and a power-stage amplifier to have respectivedifferent gains, or alternatively one of the differential amplifiers 4 aand 4 b is caused to have a variable gain, and thus versatility isincreased.

Note that, when a differential amplifier is divided into multiplestages, the number of stages is not limited to two as described above,and a multi-stage configuration composed of three or more stages can beemployed. In this case, a plurality of differential amplifiers areconnected to each other via the third transformer 12 to form multiplestages. This enables much higher output power than the two-stageconfiguration illustrated in FIG. 13.

Furthermore, although, in the fifth embodiment, the example has beendescribed in which the differential amplifier is divided into multiplestages in the configuration in which the matching network 100 isincluded, the differential amplifier can be divided into multiple stagesin the configuration in which the matching network 100 a, 100 b, or 100c is included.

In the above-described power amplifier circuits 1, 1 a, 1 b, 1 c, and 1d according to the first to fifth embodiments, at least the differentialamplifier 4 or at least the differential amplifiers 4 a and 4 b, atleast the first and second transformers 5 and 6 and/or at least thethird transformer 12, and at least the matching network 100, 100 a, 100b, or 100 c are mounted on the same semiconductor chip, thereby enablinga reduction in the size or cost of each of the power amplifier circuits1, 1 a, 1 b, 1 c, and 1 d.

The above-described embodiments are intended to facilitate understandingof the present disclosure but are not intended for a limitedinterpretation of the present disclosure. The present disclosure can bechanged or improved without necessarily departing from the gist thereofand includes equivalents thereof.

Furthermore, the present disclosure can take the followingconfigurations.

(1) A matching network according to one embodiment of the presentdisclosure is a matching network of a power amplifier circuit to which ahigh-frequency signal is input from an input node and that outputs, toan output node, a signal obtained by a differential amplifier amplifyingpower of the high-frequency signal. The matching network includes aninput-side winding connected between differential outputs of thedifferential amplifier; an output-side winding that is coupled to theinput-side winding via an electromagnetic field and whose one end isconnected to a reference potential; a first LC series resonant circuitincluding a capacitive element and an inductive element connected inseries with each other, and being connected in parallel with theinput-side winding; and a second LC series resonant circuit including acapacitive element and an inductive element connected in series witheach other, and being connected in parallel with the output-sidewinding.

In this configuration, resonant frequencies of the first LC seriesresonant circuit and the second LC series resonant circuit are caused tocoincide with the frequency of any harmonic of a plurality of harmonics,and thus the matching network can effectively suppress a harmonic outputfrom the power amplifier circuit.

(2) In the matching network in the above (1), a resonant frequency ofthe first LC series resonant circuit may be set in a first frequencyband including any one of odd harmonics of a plurality of harmonicsincluded in the high-frequency signal, and a resonant frequency of thesecond LC series resonant circuit may be set in a second frequency bandincluding any one of the harmonics.

In this configuration, the first LC series resonant circuit attenuatesany one of the odd harmonics, and the second LC series resonant circuitattenuates any one of the harmonics. Thus, the matching network caninhibit any one of the odd harmonics and any one of the harmonics frombeing output from the power amplifier circuit.

(3) In the matching network in the above (1), a resonant frequency ofthe first LC series resonant circuit may be set in a first frequencyband including a third harmonic.

In this configuration, the first LC series resonant circuit attenuatesthe third harmonic. Thus, the matching network can inhibit the thirdharmonic from being output from the power amplifier circuit.Furthermore, a load impedance seen from the differential amplifier isopen-circuited at even harmonics including a second harmonic by thedifferential operation of the differential amplifier and isshort-circuited at the third harmonic by the first LC series resonantcircuit. Thus, the differential amplifier performs inverse class-Foperation, thereby enabling highly efficient operation.

(4) In the matching network in the above (1) or (3), a resonantfrequency of the second LC series resonant circuit may be set in asecond frequency band including a second harmonic.

In this configuration, the second LC series resonant circuit attenuatesthe second harmonic. Thus, the matching network can inhibit the secondharmonic from being output from the power amplifier circuit.

(5) The matching network in any of the above (1) to (4) may furtherinclude an LC parallel resonant circuit including a capacitive elementand an inductive element connected in parallel with each other betweenanother end of the output-side winding and the output node.

In this configuration, a resonant frequency of the LC parallel resonantcircuit is caused to coincide with the frequency of any harmonic of aplurality of harmonics, and thus the matching network can moreeffectively suppress a harmonic output from the power amplifier circuit.

(6) In the matching network in the above (5), a resonant frequency ofthe LC parallel resonant circuit may be set in a third frequency bandincluding any one of a plurality of harmonics included in thehigh-frequency signal.

In this configuration, the LC parallel resonant circuit attenuates anyone of the plurality of harmonics. Thus, the matching network caninhibit any one of the plurality of harmonics from being output from thepower amplifier circuit.

(7) In the matching network in the above (5), a resonant frequency ofthe LC parallel resonant circuit may be set in a third frequency bandincluding a third harmonic.

In this configuration, the LC parallel resonant circuit attenuates thethird harmonic. Thus, the matching network can still more effectivelyinhibit the third harmonic from being output from the power amplifiercircuit.

(8) The matching network in any of the above (1) to (4) may furtherinclude an LC high pass filter circuit including a capacitive elementconnected between another end of the output-side winding and the outputnode, and an inductive element connected between the output node and thereference potential.

In this configuration, the LC high pass filter circuit attenuates afrequency band not higher than a cutoff frequency. Thus, the matchingnetwork can suppress low-frequency oscillation generated through apower-supply loop or the like in the power amplifier circuit.

(9) In the matching network in the above (8), a cutoff frequency of theLC high pass filter circuit may be set in a frequency band lower than afundamental of the high-frequency signal.

In this configuration, the LC high pass filter circuit attenuates afrequency band lower than the fundamental of the high-frequency signal.Thus, the matching network can suppress low-frequency oscillationgenerated through the power-supply loop or the like in the poweramplifier circuit without necessarily attenuating the fundamental of thehigh-frequency signal.

(10) The matching network in any of the above (1) to (4) may furtherinclude an LC low pass filter circuit including an inductive elementconnected between another end of the output-side winding and the outputnode, and a capacitive element connected between the output node and thereference potential.

In this configuration, the LC low pass filter circuit attenuates afrequency band not less than a cutoff frequency. Thus, the matchingnetwork can inhibit a harmonic with a frequency not less than the cutofffrequency from being output from the power amplifier circuit.

(11) In the matching network in the above (10), a cutoff frequency ofthe LC low pass filter circuit may be set in a frequency band higherthan a fundamental of the high-frequency signal.

In this configuration, the LC low pass filter circuit attenuates afrequency band higher than the fundamental of the high-frequency signal.Thus, the matching network can inhibit a harmonic with a frequency notless than the cutoff frequency from being output from the poweramplifier circuit without necessarily attenuating the fundamental of thehigh-frequency signal.

(12) A power amplifier circuit according to one embodiment of thepresent disclosure includes the matching network in any of the above (1)to (11).

In this configuration, the power amplifier circuit can inhibit aharmonic from being output.

(13) In the power amplifier circuit in the above (12), a plurality ofthe differential amplifiers may be connected to each other via atransformer to form multiple stages.

This configuration enables higher output power of the power amplifiercircuit.

(14) In the power amplifier circuit in the above (12) or (13), at leastthe differential amplifier and at least the matching network may bemounted on an identical semiconductor chip.

This configuration enables a reduction in the size or cost of the poweramplifier circuit.

The present disclosure makes it possible to suppress a harmonic outputfrom the power amplifier circuit.

While embodiments of the disclosure have been described above, it is tobe understood that variations and modifications will be apparent tothose skilled in the art without necessarily departing from the scopeand spirit of the disclosure. The scope of the disclosure, therefore, isto be determined solely by the following claims.

What is claimed is:
 1. A matching network of a power amplifier circuitthat receives, at an input node, a high-frequency signal and thatoutputs, to an output node, a signal obtained by amplifying a power ofthe high-frequency signal with a differential amplifier, the matchingnetwork comprising: an input-side winding connected between differentialoutputs of the differential amplifier; an output-side winding that iscoupled to the input-side winding via an electromagnetic field, whereina first end of the output-side winding is connected to a referencepotential; and a first LC series resonant circuit connected in parallelwith the input-side winding, the first LC series resonant circuitcomprising a first capacitive element and a first inductive elementconnected in series with each other.
 2. The matching network accordingto claim 1, wherein a resonant frequency of the first LC series resonantcircuit is in a first frequency band comprising a third harmonic of thehigh-frequency signal, and wherein a lower limit of the first frequencyband is not less than 0.85 times a frequency of the third harmonic andan upper limit of the first frequency band is not more than 1.15 timesthe frequency of the third harmonic.
 3. The matching network accordingto claim 1, further comprising: an LC parallel resonant circuitconnected to a second end of the output-side winding, wherein the LCparallel resonant circuit comprises a capacitive element and aninductive element connected in parallel with each other.
 4. The matchingnetwork according to claim 3, wherein a resonant frequency of the LCparallel resonant circuit is in a third frequency band, the thirdfrequency band comprising an harmonic of the high-frequency signal, andwherein a lower limit of the third frequency band is not less than 0.85times a frequency of the harmonic and an upper limit of the thirdfrequency band is not more than 1.15 times the frequency of theharmonic.
 5. The matching network according to claim 3, wherein aresonant frequency of the LC parallel resonant circuit is in a thirdfrequency band, the third frequency band comprising a third harmonic ofthe high-frequency signal, wherein a lower limit of the third frequencyband is not less than 0.85 times a frequency of the third harmonic andan upper limit of the third frequency band is not more than 1.15 timesthe third frequency of the harmonic.
 6. The matching network accordingto claim 1, further comprising: an LC high pass filter circuit connectedbetween a second end of the output-side winding and the referencepotential, wherein the LC high pass filter comprises a capacitiveelement connected to the second end of the output-side winding, and aninductive element.
 7. The matching network according to claim 6, whereinthe inductive element is connected between the reference potential and apath that connects the second end of the output-side winding to theoutput node.
 8. The matching network according to claim 6, wherein acutoff frequency of the LC high pass filter circuit is in a frequencyband lower than a fundamental of the high-frequency signal.
 9. Thematching network according to claim 1, further comprising: an LC lowpass filter circuit connected between a second end of the output-sidewinding and the reference potential, wherein the LC low pass filtercomprises an inductive element connected to the second end of theoutput-side winding, and a capacitive element.
 10. The matching networkaccording to claim 9, wherein the capacitive element is connectedbetween the reference potential and a path that connects the second endof the output-side winding to the output node.
 11. The matching networkaccording to claim 1, wherein a power-supply potential is connected to amidpoint of the input-side winding.
 12. The matching network accordingto claim 9, wherein a cutoff frequency of the LC low pass filter circuitis in a frequency band higher than a fundamental of the high-frequencysignal.
 13. A power amplifier circuit comprising: the matching networkaccording to claim
 1. 14. The power amplifier circuit according to claim13, comprising a plurality of the differential amplifiers connected toeach other via transformers to form multiple power amplification stages.15. The power amplifier circuit according to claim 13, wherein thedifferential amplifier and the matching network are mounted on a samesemiconductor chip.
 16. The matching network according to claim 2,further comprising: an LC parallel resonant circuit connected to asecond end of the output-side winding, wherein the LC parallel resonantcircuit comprises a capacitive element and an inductive elementconnected in parallel with each other.